This invention relates to an antenna and to a method of making such antenna and component parts thereof.
Flat panel antennas generally have one or more radiator elements or patches and a feed circuit for the patches, the patches and the feed circuit being of thin flat conductive material and being separated from a conductive ground plane by means of one or more layers of a dielectric substrate. The most common method of making such antennas involves the use of photolithographic or etching techniques on thin copper sheets laminated on microwave substrate materials. The substrate materials are relatively high loss materials and are expensive. Styrofoam has also been used as a dielectric material, but this suffers from moisture retention which is detrimental to the performance of the antenna.
It is an object of the Invention to provide an antenna construction which makes use of low cost and, in the case of the dielectric material, low loss materials, which can be die-cut with sufficient accuracy to enable repeatable high volume assembly.
According to the invention there is provided an antenna which comprises means forming a ground plane, a conductive foil element spaced from the ground plane, and a dielectric substrate separating the conductive foil element from the ground plane, the substrate being of an extruded plastics material having a cellular configuration in cross-section.
Thus, the substrate may be of the kind of extruded plastics material that comprises a pair of spaced, parallel skins and webs extending between and separating the skins. Such material is also referred to generically as xe2x80x9ccorrugated plasticxe2x80x9d because of its resemblance to corrugated cardboard. It is commonly used in the packaging and signage industries. One such type of material is available commercially in South Africa as xe2x80x9cCoruplasxe2x80x9d, which is an extruded polypropylene material.
The substrate may comprise two or more superimposed sheets of extruded plastics material, each said sheet having a pair of spaced, parallel skins and webs extending between and separating the skins.
Where the antenna includes one or more radiator elements, the conductive foil element may be configured to form a feed circuit for the radiator element or elements.
The feed circuit may be a microstrip feed circuit, or it may be a stripline feed circuit.
In another form of the invention the conductive foil element may be configured to form said radiator element or elements.
The dielectric substrate may comprise a pair of superimposed lower and upper sheets of dielectric material, each said sheet being of an extruded plastics material having a cellular configuration in cross-section, and the upper sheet having an edge which is within the periphery of the lower sheet, the conductive element being a one-piece element having a first portion which is supported by the upper face of the lower sheet, a second portion which extends up said edge to the upper face of the upper sheet, and a third portion which is supported by the upper face of the upper sheet.
In yet another form of the invention the conductive element may be a one-piece element which is configured to form said radiator element or elements and a feed circuit for the radiator element or elements.
In this event the dielectric substrate may comprise a pair of superimposed lower and upper sheets of dielectric material, each said sheet being of an extruded plastics material having a cellular configuration in cross-section, and the upper sheet having an edge which is within the periphery of the lower sheet, wherein that part of said conductive element which forms the feed circuit has a first portion which is supported by the upper face of the lower sheet and a second portion which extends up said edge to the upper face of the upper sheet, and wherein that part of said conductive element which forms the radiator element or elements is supported by the upper face of the upper sheet.
The conductive foil element may comprise a die-cut conductive foil element.
Further according to the invention there is provided a method of making an antenna having a dielectric substrate and a conductive foil element on the substrate, the foil element having a predetermined outline, which method comprises:
providing the substrate as a sheet of extruded plastics material having a cellular configuration in cross-section;
providing a sheet of conductive foil and die-cutting the foil sheet along said outline, in such a manner that bridge portions of foil remain between that part of the foil sheet which is inside the outline and that part of the foil sheet which is outside the outline;
applying the foil sheet, after it has been die-cut, to the substrate sheet, there being an adhesive between that part of the foil sheet which is inside the outline and the substrate sheet, so that that part of the foil sheet which is inside the outline becomes attached to the substrate sheets by means of the adhesive; and
thereafter removing that part of the foil sheet which is outside the outline by severing the bridge portions.
The adhesive may, prior to applying the foil sheet to the substrate sheet, be applied to the substrate sheet across a selected area corresponding roughly to the area defined by said outline.
The adhesive may be applied to the substrate sheet by means of a silk-screening process.
A protective peel-off sheet may be applied to the dielectric sheet after the adhesive has been applied to the dielectric sheet, to cover the adhesive, and the peel-off sheet subsequently, prior to applying said foil sheet, removed.
Still further according to the invention there is provided a method of making a component part of an antenna, which component part comprises a dielectric substrate and a layer of conductive foil adhered to the dielectric substrate, wherein the assembly of substrate and conductive foil layer is die-cut by means of a die-cutting apparatus having a base and a head with die-cutting blades, the head and the base moving towards one another during a die-cutting operation, and wherein said assembly is placed on the base with the side of the conductive foil layer being adjacent the base, whereby the die-cutting blades penetrate the assembly from the side of the dielectric sheet and move towards the side of the conductive foil layer.